The siting and construction of the Derbyshire Mills are tightly associated with their context. Mapping of rivers and valleys in the mid 19th century found suitable locations for weirs, water mills and associated cotton-making equipment. The stone construction and timber spans form buildings that allow efficient work within. Their sections are determined by the loadings of the machinery inside, the transmission of power, and the size of trees available to Strutt and Arkwright, pioneers of the early mill towns and cotton goods. The lower levels of the buildings are often windowless to prevent competitors seeing in and stealing the secrets of the patented equipment.